This invention relates to a process for the preparation of carboxylic acids from the corresponding isoalkyl compounds. More specifically, this invention relates to a process for the preparation of para,para'-polyphenyldicarboxylic acid. Para,para'-polyphenyldicarboxylic acid is useful as a raw material for the production of high-performance polyesters and aramid resins having high heat resistance and strength.
EPO application No. 206,543 discloses a process for coupling haloaromatic carboxylic acid compounds in the presence of carbon monoxide, an aqueous solution of an alkali metal hydroxide, and a supported palladium catalyst to form 4,4'-biphenyldicarboxylic acid. U.S. Pat. No. 3,644,506 describes a process for the preparation of aromatic carboxylic acids which comprises oxidizing aromatic compounds containing at least one methyl substituent in the presence of a cobalt, manganese, nickel, or chromium catalyst, wherein the water content of the reaction mixture is maintained at less than 0.9 percent by weight throughout the reaction period.
As illustrated in the examples hereinbefore, the syntheses of polynuclear aromatic dicarboxylic acids requires considerable effort. In view of this and other deficiencies of the aforementioned prior art processes, it is desirable to provide an alternate route for the production of polynuclear aromatic dicarboxylic acids which will simplify the synthesis of such compounds and their derivatives.